There are various types of semiconductor lasers. One example is a TJS (Transverse Junction Stripe) laser shown in FIG. 1. This TJS laser may be fabricated in the following manner. First, a magnesium-doped (Mg-doped) P-type GaAs layer 4 is grown on a semi-insulating gallium arsenide (GaAs) substrate 2 by liquid-phase epitaxy. Then, a lower tellurium-doped (Te-doped) N-type AlGaAs cladding layer 6 is grown on the Mg-doped P-type GaAs layer 4 by liquid-phase epitaxy. On the lower cladding layer 6, a Te-doped N-type AlGaAs active layer 8 is grown by liquid-phase epitaxy. Again liquid-phase epitaxy is used to grow an upper Te-doped AlGaAs cladding layer 10 on the active layer 8. Then, a Te-doped N-type GaAs layer 12 is grown on the upper cladding layer 10 by liquid-phase epitaxy. Thereafter, Zn is diffused from the top surface of the Te-doped N-type GaAs layer 12 into the structure including the GaAs layer 2, the Mg-doped P-type GaAs layer 4, the lower cladding layer 6, the active layer 8, the upper cladding layer 10, and the Te-doped N-type GaAs layer 12, so as to convert respective portions of the layers 2, 4, 6, 8, and 10 into a Zn-diffused P.sup.+ -type region 14. By this Zn diffusion, a portion of the Te-doped N-type GaAs layer 12 is converted into a Zn-doped P.sup.+ -type GaAs layer 16. Then, Zn in the Zn-diffused P.sup.+ -type region 14 and the Zn-doped P.sup.+ -type GaAs layer 16 is diffused outward of the region 14 and the layer 16 to thereby form a Zn-drive-in-diffused P-type region 18, as shown. Thereafter, that portion of the P-type region 18 which is located between the layer 12 and the layer 16, and portions of the layers 12 and 16 on opposite sides thereof are etched away, so that a Te-doped N-type GaAs layer 12a and a Zn-doped P.sup.+ -type GaAs contact layer 12b result.
In manufacturing the TJS semiconductor laser of FIG. 1, liquid-phase epitaxy is used to form the P-type GaAs layer 4, the lower cladding layer 6, the active layer 8, the upper cladding layer 10, and the N-type GaAs layer 12. However, when variations in performance and reproducibility of the semiconductor lasers are taken into consideration, it is desirable to use vapor-phase epitaxy involving thermal decomposition, such as MOMBE (metalorganic molecular beam epitaxy) and MOCVD (metalorganic chemical vapor deposition).
However, when vapor-phase epitaxy involving thermal decomposition is used, a problem occurs when the P-type GaAs layer 4 is formed. Assuming that Zn which is usable in vapor-phase epitaxy is used in place of Mg, which cannot be used in vapor-phase epitaxy, to form a Zn-doped P-type GaAs layer in place of the Mg-doped P-type GaAs layer 4 by thermal-decomposition-involving vapor-phase epitaxy, Zn would diffuse from the Zn-doped P-type GaAs layer into the GaAs layer 2 and into the Te-doped N-type AlGaAs layer 6 during the diffusion step for forming the Zn-diffused P.sup.+ -type region 14 and during the drive-in diffusion step for forming the Zn-drive-in-diffused P-type region 8, because the diffusion rate of Zn is high. This diffusion reduces the carrier concentration of the Zn-doped P-type GaAs layer.
In order to avoid this problem, the Mg-doped P-type GaAs layer 4 is formed because Mg has a low diffusion rate, but is unusable in thermal-decomposition-involving vapor-phase epitaxy.
Carbon (C) is known as a dopant which has a very low diffusion rate and is still usable in vapor-phase epitaxy in which thermal decomposition takes place. It is, therefore, desired to use C to form a P-type GaAs semiconductor layer by vapor-phase epitaxy involving thermal decomposition.
Processes for forming a P-type GaAs semiconductor, using C as a dopant, are disclosed in, for example, Japanese Published Patent Application No. SHO 62-104118 and Japanese Published Patent Application No. SHO 62-88820. According to the method of the former Japanese application, a P-type GaAs semiconductor layer is formed by MBE (molecular beam epitaxy), using trimethylgallium and arsenic as vapor sources. In the manufacturing method disclosed in Japanese Published Patent Application No. SHO 63-88820, trimethylgallium and arsine are alternately fed while a P-type GaAs semiconductor layer is being formed by MOCVD.
However, the method disclosed in Japanese Published Patent Application No. SHO 62-104118 has disadvantages that processes other than MBE cannot be used and that adjustment of the concentration of C is difficult. A problem encountered in the process of Japanese Published Patent Application No. SHO 63-88820 is that although adjustment of the concentration of C is possible, the manufacturing process is complicated since it is necessary to alternately supply trimethylgallium and arsine.
An object of the present invention is to provide a method of making P-type gallium arsenide semiconductor, using C as a dopant.
Another object of the present invention is to provide a semiconductor light-emitting device in which a P-type gallium arsenide semiconductor layer doped with C is incorporated as part thereof, and also a method of making such a semiconductor light-emitting device.